Post on 16-Mar-2020
Earth in SpaceCHAPTER 19 – LESSON 1
What causes the cycle of seasons
on Earth?
Your prior knowledge is what you already know
before you read about a topic. Before you
read, write what you know about seasons on
Earth in the graphic organizer. As you read write
down what you learn.
Share ideas.
Building Background
What time does the sun rise in the morning
and set at night?
Describe how the number of hours of
daylight changes during the winter and
summer.
Why does all of this happen?
Earth’s Rotation
Axis: the imaginary line that passes through Earth’s center and the
North and South poles.
Rotation: the spinning of Earth on its axis.
Earth’s rotation is what causes night and day.
The Earth rotates from West to East.
It takes the Earth 24 hours to rotate once – this is
Earth’s Revolution
Earth also travels around the sun. This movement is called a
Revolution: the movement of one object around another.
It takes the Earth 365.25 days (or 1 year) to make one revolution
around the Sun.
Earth’s orbit around the sun is shaped like an ellipse (oval).
Earth’s Revolution
What is a leap year?
Why do leap years occur?
Earth’s Seasons
Sunlight hits the Earth at different angles.
Near the Equator gets the direct sunlight and the further you move
away from the Equator (toward the Poles) the less direct sunlight you get).
This means that the closer you are to the Equator the warmer the
climate is and the farther away you are the colder the climate is.
Earth’s Seasons
Based on the information that was just presented, what do you think
causes Earth’s seasons?
Earth’s Seasons
Earth has seasons because its axis is tilted as it revolves around the
sun.
As Earth revolves around the sun, the north end of its axis is tilted away from the sun for part of the year and toward the sun for part
of the year. The same is true for the south end of its axis.
Summer and Winter are caused by Earth’s tilt as it revolves around
the Sun. The change in seasons is NOT caused by the change in
Earth’s distance from the sun.
Earth’s Seasons
Earth’s Seasons - Solstices
Solstices: when the sun is farthest north or south of the equator
Occurs twice a year
Summer Solstice
Occurs June 21
Longest day of the year (daytime longer than nighttime)
Northern hemisphere is tilted toward the sun.
Winter Solstice
Occurs December 21
Shortest day of the year (daytime shorter than nighttime)
Southern hemisphere is tilted toward the sun.
Earth’s Seasons - Equinoxes
Equinox – when neither hemisphere is tilted toward or away from the
sun.
Occurs twice a year.
Vernal (Spring) Equinox
March 21
Daytime = Nighttime
Autumnal Equinox
September 22
Daytime = Nighttime
Earth’s Seasons
How are the solstices and equinoxes
related to the seasons?
How would the seasons be different if
Earth were not tilted on its axis?